This section contains the detail about theevent handling in java Swing.
Working with event handling
? An object that describes a change of state in a source component is called
an event.
? The source components can be the elements of the Graphical User
Interface(GUI).
? Events are supported by the classes and interfaces defined in the
'java.awt.event' package.
? Identifying the Source Of Events:
? An event source is an object that generates an event.
? An event source registers some listeners, which receive notifications about a
specific type of event generated by that particular event source.
? All the registered listeners are notified about the generation of an event and
receive a copy of the event object.
? This is known as multicasting the event.
? Some sources allow only single listener to register.
? This is known as unicasting of event.
Given below various event sources and the types of events they generate :
| Event Source | Description |
| Checkbox | Creates an item event when a check box is selected or deselected. |
| Button | Creates an action event when a button is pressed. |
| List | Creates an action event when an item is double-clicked; creates an item event when an item is selected or deselected. |
| Scrollbar | Creates an adjustment event when a scroll bar is scrolled. |
| Text components | Creates a text event when a text character is entered in the text component. |
| Window | Creates a window event when a window is activated, deactivated, opened, closed, or quit. |
Event Listeners and Event Handlers
? An event listener listens for a specific event and is notified when that
specific event occurs.
? An event listener registers with one or more event sources to receive
notifications about specific types of events and processes the events.
? An event-handler is called by the event listener whenever a specific event
occurs.
? Event listeners are interfaces and the event-handler is a method declared in
the event listener interface that is implemented by the application.
? The syntax of a method that registers an event listener with an event source
is:
public void addTYPEListener(TYPEListener obj)
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